I recently did a DIY 3rd function and added a grapple for my little LX3310. I went with 3/8" flat face fittings and the more I use them the more I like them. When I take all the pressure off to disconnect I just plug the two grapple fittings together. It seems every time I remove and install it the fittings get easier to connect and virtually no fluid loss when doing it.
1/4" flat face are less common but sufficient for a grapple. I mainly went with 3/8" because I wanted maximum flow to operate a mower I adapted.